Radio Frequency Identification (RFID) technologies are widely used for automatic identification. A basic RFID system includes an RFID tag or transponder carrying identification data and an RFID interrogator or reader that reads and/or writes the identification data. An RFID tag typically includes a microchip for data storage and processing, and a coupling element, such as an antenna, for communication. An RFID reader operates by writing data into the tags or interrogating tags for their data through a radio-frequency (RF) interface. During interrogation, the reader forms and transmits RF waves, which are used by tags to generate response data according to information stored therein. The reader also detects reflected or backscattered signals from the tags at the same frequency, or, in the case of a chirped interrogation waveform, at a slightly different frequency.
RF readers can operate at a number of different frequency bands or ranges. Common low frequency ranges include 125–134 KHz and 13.56 MHz, and common high frequency or ultra-high frequency (UHF) ranges include 860–960 MHz, and 2.4–2.5 GHz. RFID systems operating at the low-frequency ranges are widely used and are inexpensive, but have the fundamental disadvantage that coupling between the reader antenna and the tag antenna is almost entirely inductive. As a consequence, the power that can be coupled to the tag falls rapidly when the distance between the reader and the tag is greater than roughly the antenna size. Since the reader antenna size is typically limited to around 1 meter, an interrogation range characterized by a maximum operable reader-tag separation in low-frequency systems is similarly limited to less than about 1 meter, with typical interrogation range for high data rate applications being even shorter (e.g., a few tens of cm). This interrogation range, although limited, still allows many useful applications, but when longer interrogation range is required, it is appropriate to consider UHF (i.e., 900 MHz or higher) systems, which allows much longer interrogation ranges, such as from about 3 to 8 meters, to be achieved.
Conventional RFID readers operating at the UHF frequency band around 900 MHz have been large, separately packaged devices attached to removable external antennas or integrated with an antenna. Examples of these readers include the ALR9780 and ALR 9040 readers from Alien Technology, the AR400 and SR400 devices from Matrics/Symbol, and the ITRF and IF5 readers from Intermec Inc. Relatively large handheld readers with integral antennas have also been reported, such as the IP3 and Sabre 1555 devices from Intermec Inc.
RFID readers have not been made in a PC Card format so that it can be integrated in handheld, portable or laptop computers to read from and write to RFID tags. It is apparent that incorporation of a RFID reader into a PCMCIA-compatible (“PC-card”) form factor will provide numerous practical advantages, since a user may then employ the PC-card-reader in any PC-card-compatible device, such as a laptop computer, or personal digital assistant (PDA), with only the addition of appropriate software. In this fashion virtually any portable computing device can be RFID-enabled. The flexibility of an RFID reader on a PC Card also allows easy integration of an intelligent long-range (ILR) system into enterprise systems and permits combination with other technologies such as bar code and wireless local area networks (LAN). The making of a PC Card RFID reader, however, presents many challenges, one of them is associated with the design of a suitable antenna.